The present invention generally relates to the surface mounting of integrated circuit (IC) devices to a printed circuit (PC) board, and more particularly to test sockets for the test and burn-in of IC devices. The invention is particuarly suited to the testing of leadless IC chips, but is not limited to such applications.
The increased capabilities of IC chips have led to increased input/output (I/O) densities and alternative techniques for mounting IC chips to printed circuit (PC) boards involving leadless IC chips. For example, ball grid array (BGA) mounting techniques have been developed to replace pin grid array (PGA) mounting approaches in order to achieve more densely packed contacts and smaller contact dimensions (in the order of 25 mils.). To facilitate the testing and burn-in of leadless IC devices, special test sockets have been devised to hold these devices and to temporarily connect them to a PC test board. Test sockets for leadless IC devices most commonly employ stamped or formed metal contact pins for achieving electrical interconnection between the I/O contacts of the IC device being tested and the PC test board circuits. Such socket designs have a relatively high profile and relatively high capacitance and inductance making them undesirable for high speed applications. They also require soldering of the socket pins to the PC board and do not operate efficiently with IC devices having noncompliant I/O contacts. Sockets having elastomeric contactors which do not require soldering have also been devised. These test sockets utilize flexible wire filaments which extend in a perpendicular relation to the contact points. Such wire filaments are generally not reliable and will not hold up with repetitive use. In addition, they are not likely to withstand the thermal shock while testing an IC device.
Still another known IC test socket design is a test socket having high profile, spring-loaded pins, called xe2x80x9cpogo pins.xe2x80x9d Heretofore, the use of pogo pins in test sockets have been limited to relatively long, single-ended pogo pins wherein one end of each pogo pin is a fixed end soldered to the PC board and the other end is spring-loaded. Again, the relatively high profile of such test sockets make them unsuitable for high speed test applications. Also, since the fixed ends of the pogo pins are soldered to the PC board, such sockets are relatively difficult to remove.
The present invention overcomes the disadvantages of conventional test sockets for leadless IC devices by providing a low profile test socket suitable for high frequency test applications which will provide efficient and solderless contacts for both the PC board and the IC devices being tested.
Briefly, the present invention provides for an improved IC socket for surface mounting an IC device having a predetermined array of I/O contacts to a circuit board having a corresponding array of circuit contacts using an array of miniature, double-ended pogo pins which provide an array of resilient contacts for both the circuit contacts of the PC board and the I/O contacts of the IC device. More specifically, the IC socket has a body portion which includes a contact interface wall having opposed and substantially parallel mounting surfaces, one of the mounting surfaces of the interface wall is an interior mounting surface for receiving an IC device and the other of the mounting surfaces being an exterior surface for mounting the body portion of the socket to the circuit board. A plurality of substantially parallel conductor pins in the form of double-ended pogo pins extend through and are held by the contact interface wall in an array that corresponds to the predetermined array of the I/O contacts of the IC device (as well as to the corresponding circuit contacts of the circuit board). The conductor pins, which have contact ends that project beyond the mounting surfaces of the contact interface wall, provide a conductive path between these mounting surfaces. By using double-ended pogo pins, both contact ends of the pins will be resiliently depressible to provide spring-loaded contacts for both the IC device held in the socket and the circuit board to which the socket is mounted. Means for releasably holding an IC device against the interior mounting surface of the contact interface wall of the socket""s body portion is provided such that the I/O contacts of the IC device remain in contact with the ends of the conductor pins at all times.
It is noted that the invention""s substantially parallel conductor pin provide a conductor pin footprint that is the same on both sides of the socket. Thus, the socket receives an IC device having the same contact footprint as the contact footprint on the PC board to which it is mounted. This permits the IC device to be soldered directly to the PC board after the test socket, which is not soldered to the PC board, is removed.
Therefore, it can be seen that a primary object of the present invention is to provide an IC test socket suitable for high frequency applications and which provides efficient electrical contacts to both the I/O contacts of an IC device and the circuit contacts of a PC board. Another object of the invention is to provide a durable test socket that can withstand the thermal shock encountered in test and burn-in applications, and that can further withstand the repeated insertions and extractions of IC devices into and from the test socket. It is still another object of the invention to provide a test socket for an IC device having the same I/O contact footprint as the footprint of the circuit contacts (also called xe2x80x9cpadsxe2x80x9d) of the PC board to which it is mounted. Yet other objects of the invention will be apparent from the following specification and claims.